This study aims to recruit 786 subjects who are eligible for inclusion in the modified intent-to-treat analysis. The study compares the efficacy, the safety and tolerance, the survival, the incidence of breakthrough deeply invasive fungal infections and the time to defervescence of voriconazole versus Ambisome, in the empirical treatment of fungal infections in immunocompromised patients with persistent fever and neutropenia. The majority of the subjects enrolled in this study will be treated with empirical antifungal medication until recovery from neutropenia (typically two weeks), with a follow-up clinical assessment seven days after the last dose of empirical therapy. Subjects who are diagnosed with a deeply invasive fungal infection can be treated until resolution of the infection up to a maximum of twelve weeks. Patients meeting all inclusion/exclusion criteria will be randomly assigned to receive treatment with either IV voriconazole for at least 3 days, followed by oral voriconazole, until recovery from neutropenia or IV AmBisome until recovery from neutropenia. Patients will be hospitalized at the beginning of study treatment and will remain until recovery from neutropenia. Assessments will be performed weekly until recovery from neutropenia. Patients without baseline or breakthrough deeply invasive fungal infections will have additional assessments performed every four weeks while on study medication, at the end of treatment, and at four weeks after the end of treatment. Evaluations will include hospitalizations, concomitant illnesses, ophthalmological safety assessment, adverse events, concurrent medications, vital signs, and laboratory analysis.